Seasonal Variations
The analysis has shown large seasonal variations in the occurrence of rainfall over
Sahibi Basin during 1961–2017. The mean rainfall during monsoon, pre-monsoon,
winter, and post-monsoon seasons is about 554 mm (SD ¼ 197.23, CV ¼ 35.60),
38 mm (SD ¼ 36.02, CV ¼ 95.36), 22 mm (SD ¼ 23.55, CV ¼ 104.84), and 20 mm
(SD ¼ 28.78, CV ¼ 146.28), respectively (Table 12.2). This analysis indicates that
the monsoon season alone contributes about 87% to the mean annual rainfall,
whereas the contribution of pre-monsoon, winter, and post-monsoon season rainfall
is about 6%, 4%, and 3%, respectively.
The season-wise mean annual variations are shown in Fig. 12.4a–d. The mean
seasonal rainfall has shown a slightly rising trend during winter and pre-monsoon
seasons while the monsoon and post-monsoon seasons have shown slightly decreasing trends. Among these trends, the pre-monsoon season trend was found to be
statistically significant (Table 12.2). These findings are consistent with those of
Kumar and Jain (2011) and Bisht et al. (2018). Further, the trend line of CV values
has shown a trend of increasing rainfall during the winter season, whereas opposite
trends have been witnessed in CV values for mean rainfall in other seasons.
The station-wise seasonal analysis has shown declining trends over all stations
during the monsoon season except Bairath and Kotkasim stations, which have
experienced increasing trends (Table 12.5). However, the increasing trend is statistically significant only for Kotkasim station. Similarly, the declining trend is statistically significant only for Tapukara station. During the pre-monsoon season, all the
stations have shown a statistically significant positive trend in rainfall, except
Mundawar, Tijara, Thanagaji, and Tapukara stations. During the winter season,
only Kotkasim station has shown a statistically significant positive trend. During
the post-monsoon season, no station has shown a statistically significant declining
trend in the Sahibi Basin (Table 12.5).
Further, seven excess and seven deficient monsoon rainfall seasons have been
observed during the 57 years (Table 12.3). The annual excess and deficient rainfall
years are associated with the monsoon season excess and deficient rainfall years,
respectively. During pre-monsoon seasons, 5 rainfall excess and 4 rainfall-deficient
years have been observed. During winter and post-monsoon seasons, 8 and 5 years
have been observed as rainfall excess years, respectively. Remarkably, no rainfalldeficient years have been witnessed in these two seasons (Table 12.3).
Monthly Variations
Monthly analysis has shown that the maximum amount of rainfall occurred in
August, followed by July, September, and June (Table 12.2). The least rainfall
occurred in the month of November, followed by the months of December and
April. The months of August and July accounted for approximately 63% of total
annual rainfall. However, these months have shown nonsignificant declining trends
in amount of rainfall (Fig. 12.5). The month of June has shown a significant rising
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M. Chahal et al.
The analysis has shown large seasonal variations in the occurrence of rainfall over
Sahibi Basin during 1961–2017. The mean rainfall during monsoon, pre-monsoon,
winter, and post-monsoon seasons is about 554 mm (SD ¼ 197.23, CV ¼ 35.60),
38 mm (SD ¼ 36.02, CV ¼ 95.36), 22 mm (SD ¼ 23.55, CV ¼ 104.84), and 20 mm
(SD ¼ 28.78, CV ¼ 146.28), respectively (Table 12.2). This analysis indicates that
the monsoon season alone contributes about 87% to the mean annual rainfall,
whereas the contribution of pre-monsoon, winter, and post-monsoon season rainfall
is about 6%, 4%, and 3%, respectively.
The season-wise mean annual variations are shown in Fig. 12.4a–d. The mean
seasonal rainfall has shown a slightly rising trend during winter and pre-monsoon
seasons while the monsoon and post-monsoon seasons have shown slightly decreasing trends. Among these trends, the pre-monsoon season trend was found to be
statistically significant (Table 12.2). These findings are consistent with those of
Kumar and Jain (2011) and Bisht et al. (2018). Further, the trend line of CV values
has shown a trend of increasing rainfall during the winter season, whereas opposite
trends have been witnessed in CV values for mean rainfall in other seasons.
The station-wise seasonal analysis has shown declining trends over all stations
during the monsoon season except Bairath and Kotkasim stations, which have
experienced increasing trends (Table 12.5). However, the increasing trend is statistically significant only for Kotkasim station. Similarly, the declining trend is statistically significant only for Tapukara station. During the pre-monsoon season, all the
stations have shown a statistically significant positive trend in rainfall, except
Mundawar, Tijara, Thanagaji, and Tapukara stations. During the winter season,
only Kotkasim station has shown a statistically significant positive trend. During
the post-monsoon season, no station has shown a statistically significant declining
trend in the Sahibi Basin (Table 12.5).
Further, seven excess and seven deficient monsoon rainfall seasons have been
observed during the 57 years (Table 12.3). The annual excess and deficient rainfall
years are associated with the monsoon season excess and deficient rainfall years,
respectively. During pre-monsoon seasons, 5 rainfall excess and 4 rainfall-deficient
years have been observed. During winter and post-monsoon seasons, 8 and 5 years
have been observed as rainfall excess years, respectively. Remarkably, no rainfalldeficient years have been witnessed in these two seasons (Table 12.3).
Monthly Variations
Monthly analysis has shown that the maximum amount of rainfall occurred in
August, followed by July, September, and June (Table 12.2). The least rainfall
occurred in the month of November, followed by the months of December and
April. The months of August and July accounted for approximately 63% of total
annual rainfall. However, these months have shown nonsignificant declining trends
in amount of rainfall (Fig. 12.5). The month of June has shown a significant rising
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